Methods for selective plugging

ABSTRACT

Methods and compositions are provided for selectively plugging the water-rich strata of subterranean formations, including the injection into the formation of a water-soluble, oil-insoluble soap or ester. The soap or ester chemically reacts in the formation, either with reactants already in the formation or reactants which may be injected along with or prior to the soap or ester, to produce a water-insoluble, oil-soluble product which is effective to selectively plug the water-rich strata over a relatively long distance and over a relatively long period of time.

United States Patent 1191 Friedman May 2 1, 1974 [5 METHODS FOR SELECTIVE PLUGGING 3,616,856 11/1971 Knight 166/288 3,620,302 11/197] F 166/288 [75] Inventor Robe" Ffledman, Housmm 3,669,188 6/1972 c1513"; al. 166/288 [73] Assignee: Getty Oil Company, Los Angeles,

m Primary Examiner-Henry C. Sutherland Assistant Examiner-Jack E. Ebel [22] Ffled: July 1972 Attorney, Agent, or Firm-Arnold, White & Durkee 21 Appl. NO.Z 270,244

[57] ABSTRACT [52] U s 166/288 166/294 Methods and compositions are provided for selectively [51] Ezlb 33/13 plugging the water-rich strata of subterranean forma- [58] Fieid 292 295 tions, including the injection into the formation of a 166/306 water-soluble, oil-insoluble soap or ester. The soap or ester chemically reacts in the formation, either with [56] References Cited reactants already in the formation or reactants which may be injected along with or prior to the soap or es- UNITED STATES PATENTS ter, to produce a water-insoluble, oil-soluble product 2,708,974 5/l955 Fischer et 3|. 166/295 is effective to selectively the wateprich 29791431 5/ 1937 strata over a relatively long distance and over a relatively long period of time. 2:238:930 4/1941 4 Claims, No Drawings 1 METHODS FOR SELECTIVE PLUGGING BACKGROUND OF THE INVENTION In the drilling and production of fluid mineral deposits such as petroleum oil and gas from subterranean formations, the presence of water has been a continuing problem. In almost every subterranean formation wherein either petroleum oil or gas (hereinafter oil) is present in quantities which make production practical, water is also present. Usually, certain portions or strata of an oil-bearing formation may be considered oil-rich, and other portions or strata of the formation may be considered water-rich. For definition purposes of this application, those portions or strata containing more than about 45 percent oil will be termed oilrich," and those containing less than about 30 percent oil will be termed water-rich. Those portions or strata having an oil concentration of between about 30 percent and about 45 percent will be termed mixed strata.

The connate water of the formation varies in mineral content from one location to another. Such water is frequently an aqueous brine solution. In many locations, the connate water contains magnesium and/or other metal salts.

Production of connate water along with oil from a producing formation is not desired for many reasons, among them being the extra production expenses encountered, the necessity for separation of the oil and water following production, and the fact that means must be provided for getting rid of undesired brackish water which is a pollutant to the surrounding terrain.

The disadvantages of producing water with oil as mentioned above are relatively insignificant compared to the disadvantages faced when certain post-primary recovery processes, such as water-flood operations, are

utilized in such formations. In accordance with such processes, it is customary to inject a driving fluid through one or more injection wells, and to produce oil through one or more producing wells. The well fluids are pushed by the driving fluids through the formation from the area of the injection wells to the area of the producing wells. By the very nature of such processes, a relatively large amount of the injected fluids will be produced at the producing well or wells. It is thus imperative that enough oil be produced through the producing wells along with the water (connate and injected) to make the process economical.

Another factor existingin many subterranean formations seriously complicates the undesired presence of water, i.e., the existence, within the formation, of gross differences in permeability. As is pointed out in the copending application of Friedman, Ser. No. 152,411, filed June 1 l, 1971, oil-bearing formations cannot be considered as having a homogeneous nature. It is well known that permeability profiles of pay sands show irregularities both horizontally and vertically. Oilbearing strata may be separated by shale streaks which prevent vertical migration between them and provide independent paths between injection wells and producing wells. These independent paths will likely have differing effective permeabilities and generally speaking the water-rich portions or strata will be the more porous strata.

These and other factors result in the watering out of certain portions of an oil-bearing formation prior to the watering out of other portions during waterflooding. When this occurs, water passing through a watered-out stratum results in oil production at increasingly unfavorable water-to-oil ratios. This water by-passing often becomes a. controlling factor in determining the final recovery which may be obtained economically by water-flooding operations. This is particularly true when the oil sand is highly heterogeneous.

The shape of the reservoir which is swept by an advancing front of injected fluid may be such that large quantities of theoretically recoverable oil will not be affected by a fluid flood. Thus, such oil might not be recovered because the flooding medium is preferentially channeled into other parts of the formation. Studies of reservoirs after waterflooding have indicated that twothirds of the residual oil is frequently located in portions of the reservoir which waterflooding has not reached, while in the water-swept portions oil content may be near the irreducible medium.

The economic significance of recovery operations of this type is great, and the problems as described above have been well recognized by the oil and gas production industry for many years. Many efforts have been made to solve the problemsin whole or in part.

Generally speaking, there have been two basic approaches to the solution of the problem. One such approach is to seal off the water-rich strata at or adjacent to the borehole, as by the use of Portland cement. This method has proved satisfactory in some instances, but is most unsatisfactory and completely impractical in others, especially in many situations wherein there is significant vertical permeability between the various strata of a formation.

Another approach suggested in the art is to selectively plug the more porous water-rich strata so that water from these strata will notbe selectively produced or selectively swept by .the driving fluid used in the post-primary process, or at least so that the oil-to-water ratio will be improved. The present invention is directed to this latter method, which is often called selective plugging.

Various solutions have been proposed by the prior art for selectively plugging porous water-rich strata. A discussion of some of these prior art methods is found in the copending application of Friedman et al., Ser. No. 152,277, filed June 1 l, 1971, which relates to a selective plugging method and composition comprising in a preferred embodiment, sodium carboxymethylcellulose, chromium potassium sulfate, and orthocresol;

Some of the prior art solutions have been successful under certain conditions, but the need remains for other practical and inexpensive solutions to these long felt problems. Especially the need remains for a selective plugging composition and method which will gradually plug and is effective over a large area or distance. Many of the selective plugging methods and compositions of the prior art have suffered from the defect that even though they may have plugged well, they did so only over a small area, thereby allowingthe driving fluid in a post-primary process to by-pass the plugged portion and then re-enter the porous water-rich strata to present the same problem as outlined above.

Because of the expense of most potential injection fluids when compared to the oil which may be recovered, many such fluids are not practical or economical for'use even though they may be technically efficient.

Consequently, the need especially exists for a selective plugging composition and method of the type described above, which additionally is sufficiently inexpensive to justify its use.

Solutions to the above long-felt problems are provided by this invention.

SUMMARY OF THE INVENTION This invention relates to selective plugging methods and compositions, wherein an inexpensive watersoluble, oil-insoluble soap or ester, or combination thereof, is injected into a subterranean formation. The

soap or ester chemically reacts in the formation to produce a water-insoluble, oil-soluble soap or acid, which is effective over a relatively long period of time to selectively plug the water-rich portions of the formation over a relatively large area.

In one embodiment of the invention, a water-soluble soap is injected which reacts with metal ions in the connate water of the formation to yield a water-insoluble, oil-soluble soap.

In another embodiment similar to the first, metal ions in the form of a metal salt or otherwise are injected into the formation, and then a water-soluble soap isinjected which reacts with those metal ions to yield a waterinsoluble, oil-soluble soap.

In another embodiment, metal ions are injected as in the previously-mentioned embodiment, but in this embodiment are injected simultaneously with the watersoluble soap. In order to prevent premature reaction, the metal ions are complexed so that reaction will occur only at the elevated temperatures in the formation.

In still another embodiment, a water-soluble soap of a first water-insoluble acid is injected along with an ester of a stronger acid. The ester is hydrolyzed to yield the strong acid, which then reacts with the water soluble soap to yield the parent water-insoluble acid of the soap.

In all embodiments, the water-insoluble, oil-soluble soaps or acids formed by the reactions specified, are effective as economical selective plugging agents which react slowly and plug a large area of the porous waterrich strata of the formation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The invention relates to selective plugging compositions and methods, which are effective to selectively plug a relatively large distance or area of a porous water-rich strata or portion of a formation, the plugging occurring over a relatively long time span.

The compositions provided comprise water-soluble soaps; in each instance these water-soluble soaps react in the fomiation to produce the plugging agent which may be a water-insoluble soap or acid.

The invention will be described in terms of several particularly preferred embodiments, which represent the best mode of the invention as known to the inventors at the time of this application.

In accordance with a first embodiment of the invention, a water-soluble soap is reacted with metal ions present in the connate water of the formation to yield a water-insoluble soap. It is quite common for connate of many formations also contains other available metal ions, such as magnesium ions.

There are certain readily available and inexpensive highmolecular weight acids which form water-soluble soaps with certain metals, and water-insoluble soaps with other metals. For example, abietic acid, C I-I COOI-I (with a phenanthrene ring system) is the major active ingredient of rosin, and is available as inexpensive commercial rosin. Abietic acid is not soluble in water, but the sodium soap, sodium abietate, is water soluble. Abietic acid is soluble in organic solvents.

The magnesium soap of abietic acid, magnesium abietate, is not water soluble, and this soap has been found to give superior results as a selective plugging agent. It plugs over a relatively long time, a relatively large distance, and its formation as indicated in this embodiment is extremely simple and inexpensive.

Thus, in a formation containing available magnesium ions in the connate water, the sodium soap of abietic acid may be injected into the formation whereupon the magnesium ions will react with the sodium soap, to produce the magnesium soap of abietic acid, which is water-insoluble, oil-soluble, and which is quite effective as a selective plugging composition.

As another example, the sodium soap of behenic acid, CH (Ch COOH, is water-insoluble although the potassium soap is water-soluble. Thus, by injecting the potassium soap of behenic acid into a formation containing available sodium ions, a reaction will occur which will yield the water-insoluble sodium soap which is effective as a selective plugging agent with the advantagesdescribed above.

The choice of the particular metal ions for any given situation will depend on a number of factors such as availability, cost (if added), and nature of, the soap formed. For example, at low temperatures the magnesium soap of rosin is generally preferred over the calcium soap. However, calcium is preferred at temperatures above about 180F, since the magnesium soap becomes too water soluble.

In accordance with another embodiment of the invention, when metal ions of the type described are not readily available in the proper location in the formation, metal ions as in the form of a metal salt may be injected into the formation prior to the injection of the water-soluble soap. Thus, for example, magnesium chloride could be injected prior to injection of sodium abietate.

In accordance with another embodiment of the invention, the metal ions are injected along with the water-soluble soap. In order to prevent premature reaction of the metal ions with the soap, the metal ions are complexed so that they will not be free to react until the constituents are downhole.

For one example, if nickel ions are not present in the formation and it is desired to form the water-insoluble nickel soap of abietic acid, nickel may be complexed with ethylenediamine, Nl-I CH CH NI-I, by adding nickel in powdered or other suitable form to the liquid ethylenediamine. The complexed nickel is thus not available to react with sodium abietate before the constituents. are injected into the formation. After entry into a formation in which the temperature is at least about F, however, the nickel ethylenediamine complex breaks down freeing nickel ions for reaction with the sodium soap, to yield the nickel soap of abietic acid.-This nickel soap is water-insoluble, oil-soluble,

and is effective as a selective plugging agent with the advantages listed above.

Another example of this embodiment of the invention is provided by the use of zinc rather than nickel, with the other constituents as indicated above.

In yet another embodiment of the invention, a waterinsoluble acid is produced in the formation as a selective plugging agent, after injection of (l) a watersoluble soap of a first, water-insoluble acid, and (2) an ester of a second acid, stronger than the first acid. Upon being injected into a formation at a temperature in excess of the hydrolyzation temperature of the ester, generally about 150F, the ester will hydrolyze into its alcohol and acid constituents. The acid constituent of the ester, being stronger than the parent acid of the soap, will then react with the soap to yield the parent acid of the soap. This parent acid, being waterinsoluble and oil-soluble is effective as a plugging agent to plug over a large area and over a relatively long period of time.

Care must be exercised to assure that the original acid regenerated is one which has a sufficiently high melting point. The exact melting point necessary depends upon the temperature in the formation; in the particular formations with which applicants have worked, this temperature has been about l80F. Thus,

although pure abietic acid may have a sufficiently high melting point to be of use in a particular formation, that acid is not generally available in the pure state, and rosin acid which is commercially available has a melting point which is too low for the formations utilized by applicant. Thus, it is necessary to utilize an acid other than rosin, and applicants chose for the following example a dimerized rosin acid the principal constituent of which is dimerized abietic acid. These dimers have two acid molecules.

An example of this latter embodiment of the invention would include the injection of the sodium soap of a dimerized rosin acid, (available commercially as Dimerex from Hercules, lnc.), and ethyl acetate. Upon entering the formation at temperatures greater than about 150F, the ethyl acetate is hydrolyzed into ethyl alcohol and acetic acid. The acetic acid then reacts with the sodium soap to yield the dimerized rosin. The dimer acid is water-insoluble and oil-soluble and is effective as a selective plugging agent.

It may be desired to add a fiocculating agent, such as ammonium phosphate, to fiocculate the precipitate.

To further illustrate the invention, applicants have performed several laboratory experiments which have given surprisingly good results on permeability reduction. The examples which follow, which should not be considered as limiting the invention but rather only as exemplary of various of the embodiments, are based on those laboratory results.

In these experiments, a core of Berea sandstone was employed, the core being 2 inches long and 1% inches in diameter. This core was completely encased in a temperature-resistant epoxy resin.

Permeabilities were measured at ambient temperature, then the cores were allowed to reach equilibrium at l80F (simulating field conditions) for the experiments. Following the experiments, the cores were cooled and the permeabilities again measured at ambient temperature. The final permeability measurements were compared to the initial measurements to deterity was measured in each instance by timing the rate of flow of water through the sample, maintaining a constant pressure in the sample.

The field water employed was from the Ventura field in Southern California.

EXAMPLE I After the sandstone core had reached equilibrium at l80F, about 20 ml. of field water containing not less than 8000 mg./l. sodium, 450 mg./l. calcium, and 100 mg./ 1. magnesium, was injected into the core, followed by about one pore volume(about 3 ml.), of an aqueous solution of 0.5 percent sodium abietate prepared in deionized water.

Permeability loss was measured at 66 percent.

EXAMPLE II After the core had reached equilibrium, about 20 ml., salt water, containing not less than 20,000 mg./l. sodium chloride, was injected followed by about one pore volume (about 3 ml.) of 0.5 percent solution of potassium behenate prepared in deionized water.

Permeability loss was 48.5 percent.

EXAMPLE III A zinc ethylenediamine complex was formed by adding ethylenediamine to a concentrated solution of zinc sulfate, until the zinc precipitate completely dissolved with an excess of around 10-20 percent of the ethylenediamine. The complex was then dissolved in sodium abietate solution to give a final composition of 0.5 percent sodium abietate and 0.225 percent zinc complex (90 percent of sodium abietate stoichiometrically). Solutions of this type are stable for l 2 days at ambient temperature and for several hours at l80F.

Several pore volume (about 25 ml.) of this mixture were injected into the core. The core was allowed to stand at l80F overnight, then cooled to ambient temperature.

Permeability loss was 47 percent.

EXAMPLE IV Dymerex, a dimer acid produced from rosin available from Hercules, Inc., has a melting point of about 250F.

mine the permeability loss in each instance. Permeabil- The potassium soap of this dimer can be readily prepared. Several pore volumes (about 25 ml.) of an aqueous solution of 0.5 percent potassium Dymerex solution containing 1.5X stoichiometric ethyl acetate and a small amount of ammonium phosphate (to flocculate the precipitate) were injected into the core at lF. The core was allowed to stand at l80F overnight, then cooled to ambient temperature.

Permeability loss was measured at percent.

Table l presents a summary of laboratory experiments performed by applicant. These experiments utiv lized formation water and oil from the Ventura field in California, at a temperature of about l80F. The Ventura reservoir is a moderately saline high temperature reservoir.

Although the invention has been described in terms of particular embodiments which applicant believes to represent the best modes of the invention at the time of this application, it will be recognized by those of skill TABLE I RESULTS OF EXPERIMENTS WITH HIGH MOLECULAR WEIGHT SOAPS FOR SELECTIVE PLUGGING Process Principal Injected Reacts With Other Function of Reaction Hi" F NuCl Production Field Name Ingredient Solution Chemicals ther Product Solutton Wutcr (Trademark) Form Used Chemicals 1. Behenic Hydrofo l Potassium Sodium ion in Potassium To make Sodium ppts with over ppt Acid 2022-55 Soap salt water hydroxide K-soap behenate l0,000 ppm (Ashland Chemical) I "II Ifl I 2. Dimerized Hystrene Potassium Sodium-ions Potassium To make Sodium soap ppts With over ppt Stearic 3675C Soap in salt hydroxide -soap 35,000 ppm Acid (HUmk0) water II I MI II I I I I I I 3. Rosin Soap D'rsin-ate X X KIF Calcium or None Calcium ppts with over ppt (Hercules magnesium in rosinate 30,000 ppm Inc.) formation water g As is Zinc ion Zinc sulfate To provide Zinc rosinate ppts with over ppt released from reactant 30,000 ppm complex Ethylene-diamine To complex zinc I III 4. Modified Pentalyn 255 Potassium To make soap Modified p r with over PP Rosin (Hercules hydroxide I rosin 4 00 ppm Inc.) I 5. Modified Pentalyn 26l Potassium An acid Triacetin or To provide Modified ppts with over ppt Rosin (Hercules Soap created in situ methyl acid when rosin 40,000 ppm Inc.) formate ester hydrolyzes I I 6. Dimerized Dymerex (NHIMH POIa T flocculate Dimerized ppts wlth over ppt (Hercules (Hercules precipitate 25.000 ppm Inc.) Inc.)

Injection Field Loss of Effect on Viscosity Melting Point of Approximate comments Water Permeability in of Oil Precipitate 'Cost/bbl With 7 Core Tcst 0.5% Principal Ingredient l. None 48.5% (high Very large increase 300 F $0.55 Solution of KOH and acid requires no heat Salt) y in freshwater; 2. None 45.5%I (high No increase 300 F $0.54 Same as behenic. except soft water.

sa t) 3 ppt 66% (Field Increases slightly 300 F $0.28 'Dresinate comes slightly underbased, with 5 injection water) oz. caustic per barrel, clear solution in soft water. No heat. ppt 47% (fresh Forms fairly stable 300 F $0.67 No mixing problem in salt water. No heat water) emulsion desirable. 4. None Not tested Increases several 230 F $0.79 Can use saline water. No heat desirable.

. times 5. None Not tested Increases several 2l5 F $0.85 Same as Pentalyn 255.

- times 6. ppt 85% (fresh Increases slightly 250 F $0.70 Softened water. Requires 200F to make water) potassium soap. Cool before adding ester.

in he that various changes may be made in the composition and method embodiments of this specification without departing from the scope of the invention as defined in the following claims.

What is claimed is:

l. A method for selectively plugging water-rich strata of a relatively high-temperature subterranean-formation containing strata which are water-rich and other strata which are oil-rich, and said strata having at least one borehole therein, comprising:

providing an aqueous composi on of a water-soluble,

oil-insoluble metal soap of a high-molecular-weight' acid, and a complex of another metal;

' passing said composition into said borehole;

injecting said composition into said formation at a pressure sufficient to overcome the natural formation pressure; I I

the heat of said formation being efiective to break said metal complex to yield available ions of said other metal; reacting said soap with said metal ions to form as a reaction product, a second metal soap of said acid, said second metal soap being water-insoluble and oilsoluble, said reaction product being effective to greatly sodium soaps of abietic and behenic acid. 

2. The method in accordance with claim 1, wherein the complexed metal is selected from the group consisting of nickel and zinc.
 3. The method in accordance with claim 1, wherein said acid is selected from the group consisting of rosin, abietic and behenic.
 4. The method in accordance with claim 1, wherein said soap is selected from the group consisting of the sodium soaps of abietic and behenic acid. 